The overall framework for ISMIP6 is designed to deliver projections of the ice sheets contribution to sea level rise. Together with the CliC targeted activity on glaciers and projections of thermal expansion (that already sit within the CMIP framework), this will allow sea level to become part of the family of variables for which CMIP can provide routine IPCC-style projections.
The proposed experiments will both use and augment the CMIP6-DECK, Historical and ScenarioMIP experiments, as summarized in Table 1. ISMIP6 will use the standard CMIP AGCM and AOCGM experiments for analysis of the climate over and surrounding the ice sheets, and as forcing for the standalone ice sheet models (ISM) projections. Additional sensitivity experiments will be performed with the ISM to investigate the uncertainty associated with these projections arising from ice sheet models. The key output will be an ensemble of historical and future estimates of ice sheet contribution to sea level.
To address the feedbacks introduced by interactive ice sheets, we propose that a small number of selected DECK experiments are repeated with coupled AOGCM-ISM, where the ice sheet is an interactive component of the AOGCM. Our assessment of the state of existing AOGCMs is that coupled models including an interactive Greenland ice sheet can realistically be expected for CMIP6, however including the Antarctic ice sheet remains challenging (because of the greater complexity of its response to climate forcing, and the issues associated with simulations of the Southern Ocean). It is for these reasons that ISMIP6 heavily relies on standalone ice sheet models driven offline by CMIP6 climate models for projections of sea level.
The detailed specifics for the ISMIP6 experiment design will be provided in a paper for the CMIP6 Special Issue and in the ISMIP6 wiki. The proposal submitted to CMIP6 panel can be found here and here for more details on the ISMIP6/CMIP6 data request.